Bromocresol purple which is a dye, belongs to the triphenylmethane family specifically categorized as a triarylmethane dye. It acts as a pH indicator, showing yellow coloration below pH 5.2 and violet above pH 6.8. In its cyclic sulfonate ester form, bromocresol purple has a pKa value of 6.3. It is often prepared as a 0.04% aqueous solution. This color change is due to structural changes in the molecule, which shift between different forms depending on the pH level. 
CAS No.: 115-40-2
Synonyms: 3,3-Bis(3-bromo-4-hydroxy-5-methylphenyl)-3H-benzo[c][1,2]oxathiole 1,1-dioxide; Bromocresol purple sultone form; 5,5′-Dibromo-o-cresolsulfonphthalein; MFCD0001168; 3,3-Bis(3-bromo-4-hydroxy-5-methylphenyl)-3H-benzo[c][1,2]oxathiole 1,1-dioxide
| Physical Properties | |
| Chemical formula | C21H16Br2O5S |
| IUPAC Name | 3,3-Bis(3-bromo-4-hydroxy-5-methylphenyl)-2,1λ6-benzoxathiole-1,1(3H)-dione |
| Molecular weight | 540.2 g/mol |
| Solubility | Soluble in Water, Ethanol, Methanol, and Polar Solvents |
| Flash Point | 310.7±30.1 °C |
| Density | 1.8±0.1 g/cm³ |
| Chemical Properties | |
| Colour | Brown to Dark Orange |
| State | Solid powder |
| Melting point | 241 to 242 °C |
| LogP | Â 5.92 |
| pKa | Â 6.3 |
| Vapour Pressure | 0.0±1.7 mmHg at 25°C |
| Pictograms : |
|
| Hazard Statements : | H315: Causes skin irritation. |
| Precautionary statements : | P261: Avoid breathing dust, fumes, gas, mist, spray, or vapors. P305+P351+P338: IF IN EYES: Rinse cautiously with water for several minutes. Remove contact lenses, if present, and easy to do. Continue rinsing. |
Bromocresol purple which is a dye, belongs to the triphenylmethane family specifically categorized as a triarylmethane dye. It acts as a pH indicator, showing yellow coloration below pH 5.2 and violet above pH 6.8. In its cyclic sulfonate ester form, bromocresol purple has a pKa value of 6.3. It is often prepared as a 0.04% aqueous solution. This color change is due to structural changes in the molecule, which shift between different forms depending on the pH level.
CAS No.: 115-40-2
Synonyms: 3,3-Bis(3-bromo-4-hydroxy-5-methylphenyl)-3H-benzo[c][1,2]oxathiole 1,1-dioxide; Bromocresol purple sultone form; 5,5′-Dibromo-o-cresolsulfonphthalein; MFCD0001168; 3,3-Bis(3-bromo-4-hydroxy-5-methylphenyl)-3H-benzo[c][1,2]oxathiole 1,1-dioxide
| Physical Properties | |
| Chemical formula | C21H16Br2O5S |
| IUPAC Name | 3,3-Bis(3-bromo-4-hydroxy-5-methylphenyl)-2,1λ6-benzoxathiole-1,1(3H)-dione |
| Molecular weight | 540.2 g/mol |
| Solubility | Soluble in Water, Ethanol, Methanol, and Polar Solvents |
| Flash Point | 310.7±30.1 °C |
| Density | 1.8±0.1 g/cm³ |
| Chemical Properties | |
| Colour | Brown to Dark Orange |
| State | Solid powder |
| Melting point | 241 to 242 °C |
| LogP | Â 5.92 |
| pKa | Â 6.3 |
| Vapour Pressure | 0.0±1.7 mmHg at 25°C |
| Pictograms : |
|
| Hazard Statements : | H315: Causes skin irritation. |
| Precautionary statements : | P261: Avoid breathing dust, fumes, gas, mist, spray, or vapors. P305+P351+P338: IF IN EYES: Rinse cautiously with water for several minutes. Remove contact lenses, if present, and easy to do. Continue rinsing. |
Bromocresol purple is used primarily as a pH indicator and in medical laboratories to measure albumin levels.
The primary difference between bromocresol purple and bromocresol green lies in their pH range and color transition. Bromocresol purple changes from yellow to purple between pH 5.2 and 6.8, while bromocresol green transitions from yellow to blue between pH 3.8 and 5.4.
Bromocresol purple turns yellow due to acid production during carbohydrate fermentation, which lowers the pH. If fermentation does not occur, the medium remains purple or turns darker purple due to alkaline conditions from amino acid decarboxylation.
The principle of the Bromocresol purple method detects pH changes by indicating acidic (yellow, pH below 5.2) or alkaline (violet, pH above 6.8) conditions, helping to measure the pH of a solution or medium.
To make a bromocresol purple solution, dissolve bromocresol purple powder in distilled water. Typically, a 0.04% aqueous solution is used. Adjust the concentration as needed for specific applications.
